3.1 Overall Loss/Loudness ratings

03.503GPPTransmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) systemTS

The overall international connection involving PLMNs and the PSTN should meet the overall loudness rating (OLR) limits in ITU‑T Recommendation G.111. The national parts of the connection should therefore meet the send and receive loudness rating (SLR, RLR) limits in ITU‑T Recommendation G.121.

For the case where digital routeings are used to connect the PLMN to the international chain of circuits, the SLR and RLR of the national extension will be largely determined by the SLR and RLR of the PLMN. The limits given below are consistent with the national extension limits and long term objectives in CCITT Recommendation G.121.

The SLR and RLR values for the PLMN apply up to the POI. However, the main determining factors are the characteristics of the MS, including the analogue to digital conversion (ADC) and digital to analogue conversion (DAC). Hence, in practice, it will be convenient to specify loudness ratings to the Air Interface. For the normal case, where the PLMN introduces no additional loss between the Air Interface and the POI, the loudness ratings to the PSTN boundary (POI) will be the same as the loudness ratings measured at the Air Interface. However, in some cases loss adjustment may be needed for interworking situations in individual countries.

These values are directly applicable to the case of an MS operating in a conventional non‑mobile noise environment. Studies have shown that under the PLMN noise environment, speech levels are likely to be higher. Hence, in order to avoid clipping in the speech transcoder, the value of SLR may need to be increased.

NOTE: In annex C, measurement of SLR and RLR for handset MS is specified using sinusoidal test frequencies. This may not be the optimum method of measuring the loudness ratings because of the adaptive characteristics of the GSM speech transcoders. However the actual measurement is only performed over the linear portion of the MS. When developing the subsequent test methods for handsfree MS, in annex B and annex C, it was decided to use the artificial voice described in ITU‑T Recommendation P.50, to measure send and receive sensitivities.

3.1.1 Connections with handset MSs

The nominal values of SLR/RLR to the POI shall be:

– SLR = 8 +/‑ 3 dB;

– RLR = 2 +/‑ 3 dB.

Where a user‑controlled receiving volume control is provided, the RLR shall meet the selected nominal value for at least one setting of the control. When the control is set to maximum, the RLR shall not be less than (louder than) –13 dB.

With the volume control set to the minimum position the RLR shall not be greater than (quieter than) 18 dB.

Compliance shall be checked by the tests described in annex C, clauses C.1.1 and C.1.3.

NOTE: The mechanical design of some MSs may make it impossible to seal the earpiece to the knife edge of the ITU‑T artificial ear. Minimal additional methods may be used to provide the seal provided that they do not affect the mounting position of the MS with respect to the Mouth Reference Point and the Ear Reference Point.

3.1.2 Connections with handsfree MSs

The nominal values of SLR/RLR to/from the POI should be:

– SLR = 13 +/‑ 4 dB;

– RLR = 2 +/‑ 4 dB.

Compliance shall be checked by the tests described in annex C, clause C.1.2 and C.1.4.

Where a user controlled volume control is provided, the RLR shall meet the nominal value at one setting of the control. It is recommended that a volume control giving at least 15 dB increase from the nominal RLR (louder) is provided for handsfree units intended to work in the vehicle environment. This is to allow for the increased noise volume in a vehicle.

3.1.3 Connections with headset MSs

The SLR and RLR should be measured and computed using methods given in ITU‑T Recommendation P.38. This Recommendation currently gives a measuring technique for supra‑aural earphone and insert‑type receivers. Study is continuing on other types of earpieces in ITU‑T SGXII.

The nominal values of SLR/RLR to/from the POI should be:

– SLR = 8 +/‑ 3 dB;

– RLR = 2 +/‑ 3 dB with any volume control set to mid position.

Where a user‑controlled receiving volume control is provided, the RLR shall meet the selected nominal value for at least one setting of the control. When the control is set to maximum, the RLR shall not be less than (louder than) –13 dB.

With the volume control set to the minimum position the RLR shall not be greater than (quieter than) 18 dB.